This invention relates to an image forming apparatus such as a copier, printer, facsimile and the like. In particular, this invention relates to an electrophotographic image forming apparatus in which an image is formed by using toner to develop an electrostatic image which is formed on an image carrier.
In the electrophotographic image forming apparatus in which the image is formed by using toner to develop an electrostatic image that is formed on an image carrier thus making the image visible, the developing device must always be replenished with the necessary amount of toner in order to avoid formation of image with a low toner density due to insufficient toner amounts.
One example of recent methods for replenishing is one in which the toner is stored in a bottle-shaped toner container called a toner cartridge which is removable from the image forming apparatus, and the image forming apparatus is equipped with a detecting device for detecting the amount of toner remaining in the toner container. Also, there are some image forming apparatuses that are equipped with a door for replacing the toner container, and when the remaining toner amount detecting device detects that a small amount of toner is remaining, toner replenishing can be performed by easily replacing the toner container with a new toner container at any time without stopping the image formation operation.
Examples of the toner detecting device include one in which a light emitting element and a light receiving element are disposed so as to face each other in a toner container that is formed from a transparent material in order to directly detect the remaining amount of toner that is stored in the toner container. The remaining toner amount is then detected based on the output value from the light receiving element which received light emitted from the light emitting element.
However, this type of remaining amount detecting method has the following problem. In the case of the type of device where the toner container must be rotated in order to replenish the developing device with the toner stored in the toner container, the transparent portion of the toner container becomes stained with toner and it becomes impossible to properly detect the remaining amount of toner and errors in detection often occurs.
Thus, in order to solve this type of problem, the technology of Patent Document 1 for example, has been disclosed. In this technology, a sensor is provided which detects the density of the toner in the pattern formed on the photoreceptor, and if the output from the sensor exceeds a reference value, a determination is made that there is no toner, and the “replenish toner” display flashes and at the same time, the copying operation is stopped. The toner container is then replaced and the reset button is set to ON such the copier can once again be operated.
Also Patent Document 2 discloses technology in which an antenna which is a conductivity detecting member is disposed parallel to the development sleeve in the vicinity of the development sleeve, and by measuring the changes in the amount of toner between the development sleeve and the antenna, or in other words, the applied voltage F during use, with the applied voltage F0 at the time when there is no toner as a reference, the remaining amount of toner G during use is detected.
In addition, technology in which the remaining amount of toner is detected using a remaining amount detection sensor provided inside the toner hopper is disclosed in Patent Document 3.
[Patent Document 1] Japanese Non-examined Patent Publication No. 8-160732
[Patent Document 2] Japanese Non-examined Patent Publication No. 9-114225
[Patent Document 3] Japanese Non-examined Patent Publication No. 2003-66706
However, the technology of Patent Document 1 has a problem in that, because it is a device that detects the density of the toner of the pattern formed on the photoreceptor, when a detection is made that the toner density is low, there is already no toner stored in the toner container, and because of the extreme insufficiency of the toner in the developing device, an image having low toner density is formed. In addition, after the toner container has been replaced, the reset button must be turned on, and thus there is also the problem that operation is complex.
In Patent Document 2, because the technology is a device which detects the induced current inside the developing device, and detects whether the toner amount allows sufficient toner density to be obtained, there is a problem in that when a detection is made that the amount of toner in the developing device is insufficient, an image with a low toner density has already been formed. In addition there are problems in that the induced current detection system causes the structure of the apparatus to be complex and a special circuit is required in order to calculate the remaining amount.
Also, the technology of Patent Document 3 is a device which detects toner amount in the toner hopper, when detection is made that the toner amount in the toner hopper is small, there is already no toner stored in the toner container, and there is the problem that images with extrem toner density are formed.
That is to say, detection of remaining amount of toner in the Patent Documents 1 to 3 can be done without being affected by stains in the toner container, but they do not directly detect the amount of toner stored in the toner container. As a result, in each case, there is a problem in that when the detection is made that the amount of toner remaining is not sufficient, the toner container is already empty and images are formed in which the toner density is low. In some cases even if the toner is replenished immediately, there is the problem that time for restarting the developing device is required for obtaining an image in which the toner density is stabilized.